Can you save usernames? I don't want to retype the usernames each time.

Done and fully implemented in v4.3 coming soon

I've brought this forward. This will be in v4.3.

After reviewing and trying things out. I believe this would be a great feature to add in v5.0 instead.

Planned for v4.3.

v5.0 will solve this issue to make creation of new posts easier and faster.

Follow https://trello.com/c/9POXinV2 for progress.